1. Field of the Invention
The present invention relates to a V-shaped belt, a belt-type transmission, and a saddle-type vehicle.
2. Description of Related Art
Conventionally, a V-shaped belt having a plurality of blocks and an endless connecting member for connecting the blocks has been used for a belt-type continuously variable transmission fitted to a motor bicycle or the like. As the blocks used for such a V-shaped belt, blocks made of metal such as aluminum, blocks obtained by coating a metal molded material with a resin, or the like have been known.
The V-shaped belt is used by winding itself around sheaves (pulleys) rotating at a high speed or the like. As a result, decrease in weight of the V-shaped belt has been required to facilitate the high-speed rotation. Therefore, in order to accomplish the decrease in weight of the V-shaped belt, it has been suggested that blocks made of resin or substantial resin (hereinafter, referred to as resin blocks) are used as the blocks (for example, see Japanese Patent JP-A-2002-147553).
The V-shaped belt disclosed in Japanese Patent JP-A-2002-147553 is described with reference to FIGS. 22 and 23. As shown in FIG. 22, the V-shaped belt 100 comprises a number of resin blocks 101 arranged in a line and an endless connecting member 102. As shown in FIG. 23(b), each resin block 101 has a falling H shape as seen from the front side and grooves 105 are formed inward in both sides of each resin block 101. As shown in FIG. 22, the connecting members 102 are impacted into the grooves 105 of each resin block 101. As a result, the resin blocks 101 are connected to each other through the connecting members 102. The connecting members 102 include a rubber 103 and cores 104 buried in the rubber 103. Although not shown, the V-shaped belt 100 is wound around a primary sheave and a secondary sheave of a belt-type continuously variable transmission.
A large amount of heat is generated in the V-shaped belt 100 due to friction with the sheaves. In addition, frictional heat is generated between the resin blocks 101 and the connecting member 102. Internal heat is generated in accordance with the unevenness of the connecting members when they are wound around the sheaves and the like. Accordingly, the heat easily increases the temperature of the V-shaped belt 100.
However, resin is a material having thermal conductivity lower than that of metal. As a result, in the V-shaped belt 100 employing the resin blocks 101, since heat can easily stay in the resin blocks 101, the temperatures of the resin blocks 101 and the connecting members 102 are easily increased. Therefore, the V-shaped belt 100 is not enough from the point of view of a heat-proof characteristic.
Therefore, there was suggested a V-shaped belt with an improved heat-radiating property. In Japanese Patent JP-UM-A-61-97647, it is disclosed that a V-shaped belt having falling H-shaped resin blocks is provided with depressions recessed downward in both sides of the top surface of the resin blocks. In the V-shaped belt, since the heat-radiating area can be enlarged by the depression and the thermally conductive distance between external air and engaging portions (portions in which the resin blocks and the connecting members engage with each other) which is a frictional heat source can be reduced, efficient radiation of the frictional heat is accomplished.
However, in the V-shaped belt disclosed in Japanese Patent JP-UM-A-61-97647, since the depressions recessed downward are formed in the top surfaces of the resin blocks, the area of both side surfaces of the resin blocks which contact the sheaves is reduced. As a result, a sufficient contact area cannot be guaranteed between the V-shaped belt and the sheaves, and thus it cannot be said to provide sufficient strength. Specifically, it is difficult to maintain a high rigidity in the arrangement direction of the resin blocks (longitudinal rigidity). On the contrary, when the size of the depressions is decreased in order to maintain sufficient strength, the heat-radiating area is reduced. Accordingly, a sufficient cooling effect cannot be obtained.
In Japanese Patent JP-A-61-286638, it is disclosed that a V-shaped belt is formed by integrally vulcanizing blocks and an endless belt body, clearances are formed between the neighboring blocks, and cooling air is introduced into the clearances between the blocks. Specifically, a V-shaped belt having falling H-shaped blocks and a V-shaped belt having blocks obtained by coupling upper blocks and lower blocks each other with pins are disclosed in Japanese Patent JP-A-61-286638. In the V-shaped belt having the falling H-shaped blocks, the thickness of both lateral ends of each block is smaller than that of the center thereof, and thus a clearance is formed between the neighboring blocks at the lateral ends of the block. On the other hand, in the V-shaped belt having the blocks consisting of the upper blocks and the lower blocks, a clearance is formed not between the neighboring lower blocks but between the neighboring upper blocks.
In the V-shaped belt having the falling H-shaped blocks disclosed in Japanese Patent JP-A-61-286638, since the sufficient contact area cannot be guaranteed between the sheaves and the V-shaped belt as described above, it is difficult to maintain the sufficient strength. In addition, since the clearances between the neighboring blocks reach the belt body in the V-shaped belt, the strength of the engaging portions of the blocks with the belt body is insufficient although the blocks and the belt body are integrally vulcanized.
In the V-shaped belt having the upper blocks and the lower blocks disclosed in Japanese Patent JP-A-61-286638, the lower blocks contact the sheaves but no clearance is formed between the neighboring lower blocks. As a result, it is possible to guarantee the sufficient contact area between the sheaves and the V-shaped belt but it is difficult to obtain a sufficient cooling effect. In the V-shaped belt, some degree of cooling effect may be obtained from the upper blocks. However, since the upper blocks and the lower blocks are individual members connected to each other with the pins, the effective cooling of the upper blocks cannot necessarily guarantee the cooling of the lower blocks.
As described above, it is difficult to allow the strength and the heat-radiating property of the resin blocks to stand together in the conventional V-shaped belt.